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This invention relates to a system for automatically adjusting the clearance between the shearbar and the cutterhead of a material cutting or chopping mechanism, such as an agricultural forage harvester.
With current production forage harvesters, it has been found necessary to maintain a shearbar-cutterhead clearance of less than 0.015 inch in order to maximize machine efficiency through reduced power consumption. Various mechanisms to adjust the shearbar-cutterhead clearance are disclosed in U.S. Pat. Nos. 4,055,309; 4,190,209; 4,295,616 and 4,436,248. However, all of these mechanisms depend upon manual control of the shearbar adjustment. Magnetic-electronic shearbar-cutterhead clearance sensing systems are disclosed in U.S. Pat. Nos. 4,198,006; 4,412,212 and 4,205,797. However, these systems merely measure the shearbar-cutterhead clearance, but do not provide any means for moving the shearbar to a desired clearance.
A shearbar adjusting system has been proposed wherein the shearbar is moved by electric motors controlled by various switches and a hard-wired circuit including discrete electrical circuit components. However, in this system, the shearbar is electrically insulated from the forage harvester frame and contact between the conducting shearbar and the cutterhead is sensed when an electrical circuit is completed thereby. However, such a system is undesirable because typical insulators are destroyed by the shock and vibration to which they are exposed when they are coupled to a shearbar in a forage harvester. Furthermore, if a wire were to break in such a system, then the system would not detect shearbar-cutterhead contact and the shearbar would be driven into the cutterhead past the point of initial contact and catastrophic physical damage could result. Finally, such a system does not utilize a microprocessor, and is therefore functionally limited. For example, this proposed system does not include any means for automatic shutdown or shearbar withdrawal in the event of certain failure conditions.